Toroidal continuously variable transmission for preventing the loosening of a loading nut

ABSTRACT

A toroidal continuously variable transmission comprises a main shaft having a step section. An input disc is drivably supported on the main shaft and axially movable along the axis of the main shaft. An output disc is rotatably supported on the main shaft and located facing the input disc. A power roller is disposed between and in frictional engagement with the input disc and the output disc so as to make transmission of power from the input disc to the output disc. Belleville springs (each having a center opening) are disposed around the main shaft and located at an opposite side of the input disc with respect to the output disc so as to press the input disc toward the output disc. A loading nut is screwed on the main shaft to restrict an expansion amount of the Belleville springs. The loading nut axially faces the step section of the main shaft. A sleeve is disposed between the loading nut and the step section of the main shaft. The sleeve is separable from the loading nut. The Belleville springs are mounted on the sleeve in a manner that the sleeve passes through the central opening of each Belleville spring.

TECHNICAL FIELD

This invention relates to improvements in a toroidal continuouslyvariable transmission, and more particularly to the improvements arounda loading nut for restricting the contraction amount of bellevillesprings in order to effectively prevent the loading nut from beingloosened thereby enhancing frictional contact of input and output discsagainst a power roller.

BACKGROUND ART

In a toroidal continuously variable transmission, input and output discsare disposed on a main shaft, and a power roller is disposed between andin frictional engagement with the input and output discs. The input discis fixedly mounted through ball splines on the main shaft. Bellevillesprings are usually disposed at an opposite side of the input disc withrespect to the output disc to apply a pre-load to the input disc inorder that the input and output discs are in frictional contact with thepower roller at a suitable pressure. It is usual that the axialcontraction amount of the belleville springs are restricted by a loadingnut which is screwed on the main shaft and fixed at a position near astep section of the main shaft. Such a toroidal continuously variabletransmission is disclosed, for example, in Japanese Patent ProvisionalPublication No. 4-69439.

However, drawbacks have been encountered in the above conventionaltoroidal continuously variable transmission, as discussed below. Thatis, the toroidal continuously variable transmission of this type isarranged such that rotation of a cam flange connected to an input shaftis-transmitted through a loading cam mechanism to the input disc, andthen the rotational power of the input disc is further transmittedthrough the power roller to the output disc. Particularly in case thatthe transmission is of the double cavity type, the loading nut screwedand fixed on the main shaft is higher in rigidity (or spring constant)and difficult to have a sufficient axial length of its internal threadedportion from the viewpoint of construction of the transmission.Additionally, it is also difficult that the length of an abutting endsection (contactable with the main shaft step section) of the loadingnut is sufficiently large to compensate the tightening force of theloading nut. Under such a situation, when relative rotation (in anamount corresponding to play of each ball spline in the rotationaldirection) is made between the input disc and the loading nut while themain shaft elongates owing to a thrust under a large input torquechange, the tip end of the abutting end section of the loading nutseparates from the step section and therefore there is the fear of theloading nut being loosened.

Additionally, during operation of the above conventional transmission,the belleville springs make their axial sliding movement and axialcontraction on the cylindrical section of the loading nut, in which thecylindrical section is subjected to a large amount of wear owing tosliding contact between it and the belleville springs. In view of this,the peripheral surface portion of the cylindrical section of the loadingnut has been usually hardened, for example, by carburizing. In makingsuch a hardening processing to the loading nut, it is necessary to makea precise control in order to avoid a strength degradation (depending onhardening) of the internal thread portion of the loading nut, therebycomplicating the production process of the loading nut.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an improved toroidalcontinuously variable transmission which can effectively overcomedrawbacks encountered in conventional toroidal continuously variabletransmissions.

Another object of the present invention is to provide an improvedtoroidal continuously variable transmission which can effectivelyprevent a loading nut for restricting the axial contraction amount ofbelleville springs, from being loosened even upon a large torque changeis applied to the main shaft, thereby enhancing frictional engagement ofinput and output discs with a power roller.

A toroidal continuously variable transmission according to the presentinvention comprises a main shaft having a step section. An input disc isdrivably supported on the main shaft and movable axially along an axisof the main shaft. An output disc is rotatably supported on the mainshaft and located facing the input disc. A power roller is disposedbetween and in frictional engagement with the input disc and the outputdisc so as to make transmission of power from the input disc to theoutput disc. Belleville springs (each having a center opening) aredisposed around the main shaft and located at an opposite side of theinput disc with respect to the output disc so as to press the input disctoward the output disc. A loading nut is screwed on the main shaft torestrict a contraction amount of the Belleville springs. The loading nutaxially faces the step section of the main shaft. A sleeve is disposedbetween the loading nut and the step section of the main shaft. Thesleeve is separable from the loading nut. The belleville springs aremounted on the sleeve in a manner that the sleeve passes through thecentral opening of each Belleville spring.

By virtue of the sleeve disposed between the step section of the mainshaft and the loading nut under the contracted state so as to provideand compensate the pressure of the loading nut against the step sectionof the main shaft, a sufficient large distance for providing thepressure against the main shaft step section can be secured.Additionally, the cross-sectional area of the sleeve can be made smallerthan that of a part of the main shaft between the step section and theloading nut. As a result, the rigidity (or spring constant) of thesleeve is considerably lowered relative to that of the abutting endsection of the loading nut of the conventional transmission, so that thesleeve can be set in position in the contracted state under the actionof a compressive force applied from the loading nut. Accordingly, if themain shaft of the transmission of the present invention makes itselastic deformation and elongates upon receiving a large torque changeduring operation of the transmission, the sleeve in the contracted statemakes its axial restoration so that no space is produced between thestep section of the main shaft and the sleeve to maintain a suitablepressure of the sleeve against the annular flat surface of the mainshaft step section. Thus, the loading nut can be effectively preventedfrom being loosened.

Additionally, by virtue of the fact that the sleeve is a separate memberfrom the loading nut, it is sufficient during a production process tomake a hardening treatment only on the sleeve without making thehardening treatment on the loading nut. This simplifies the productionprocess of a loading unit including the loading nut and the sleeve.Additionally, the internal thread portion of the loading nut can beaxially deeply inserted inside the cylindrical section of the sleeve soas to increase the axial dimension thereof, thus further preventing theloading nut from being loosened.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a fragmentary longitudinal sectional view of an embodiment ofa toroidal continuously variable transmission according to the presentinvention;

FIG. 2 is a fragmentary longitudinal sectional view of a conventionaltoroidal continuously variable transmission;

FIG. 3 is a fragmentary longitudinal sectional view of anotherembodiment of the toroidal continuously variable transmission accordingto the present invention; and

FIG. 4 is a fragmentary longitudinal sectional view of an essential partof a further embodiment of the toroidal continuously variabletransmission.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1, an embodiment of a double cavity type toroidalcontinuously variable transmission according to the present invention isillustrated by the reference character T. The transmission comprises amain shaft 1. Input discs 2a, 2b are mounted on the main shaft 1respectively through ball splines Bs1, Bs2 in such a manner thattransmission of power can be made from the main shaft 1 to each inputdisc. Output discs 3a, 3b are respectively located facing the inputdiscs 2a, 2b and rotatably mounted on the main shaft 1. The output discs3a, 3b are drivingly connected to an output sleeve M in a manner totransmit power to the output sleeve M. Power or friction rollers 4a, 4bare provided in such a manner that each power roller is disposed betweenthe input disc 2a, 2b and the output disc 3a, 3b to make transmission ofpower from the input disc to the output disc. Other power or frictionrollers 5a, 5b are provided to be located such that the power rollers4a, 4b (or 5a, 5b) are generally symmetrical with respect to the mainshaft 1, though not shown.

Belleville springs 6 are disposed around the main shaft 1 to push theinput disc 2a toward the output disc 3a so as to apply a pre-load to theinput disc 2a. Belleville springs 7 are also disposed around the mainshaft 1 to push the input disc 2b toward the output disc 3b so as toapply a pre-load to the input disc 2b. Each of belleville springs 6, 7is formed with a central opening (not identified) inside which the mainshaft 1 passes. A loading nut 8 formed of steel is screwed on the mainshaft 1 and located such that the belleville springs 7 are disposedbetween it and the input disc 2b. The loading nut 8 functions torestrict an axial contraction amount of the belleville springs 7. Theaxial contraction amount of the belleville springs 7 is adjustable by aspacer t disposed in a groove of the input disc 2b and in contact withthe belleville springs 7. The loading nut 8 includes a main body section8a to which a cylindrical projection 8b is integral. The cylindricalprojection 8b projects axially from the main body section 8b toward theinput disc 2b. The loading nut 8 is formed with an internal threadportion (no numeral) engaged with the external thread portion (nonumeral) of the main shaft 1. The internal thread portion of the loadingnut extends throughout the main body section 8a and the cylindricalprojection 8b. The main body section 8a has an annular flat face (nonumeral) to which the belleville springs 7 are contacted, the annularflat face being perpendicular to the axis of the main shaft 1. Thecylindrical peripheral surface of the cylindrical projection 8b isperpendicular to the annular flat face of the main body section 8a.

An annular thin sleeve S formed of steel is disposed between a stepsection 1a of the main shaft 1 and the loading nut 8. The step section1a is located radially inward of the input disc 2b and has an annularflat face (not identified) perpendicular to the axis of the mainshaft 1. The sleeve S includes a cylindrical section S1 coaxial with themain shaft 1 and tightly fitted on the cylindrical projection 8b of theloading nut 8. An end portion of the cylindrical section S1 of thesleeve S is in contact with the annular flat face of the main bodysection 8a of the loading nut 8. The tip end of the cylindricalprojection 8b of the loading nut 8 is located axially separate from thetip end of the cylindrical section S1 of the sleeve S so as to approachthe step section 1a of the main shaft 1. In other words, the tip end ofthe cylindrical projection 8b is located at the axially central part ofthe inside of the cylindrical section S1 of the sleeve S. The sleeve Sincludes an annular flange section S2 which is integral with the otherend portion of the cylindrical section S1. The annular flange section S2is mounted on the peripheral surface of the main shaft 1. The annularflange section S2 has an annular flat face (no numeral) which isperpendicular to the axis of the main shaft 1 and in contact with theannular flat face of the step section 1a. As shown, the bellevillesprings 7 are mounted on the cylindrical section S1 of the sleeve S. Thetip end of the cylindrical projection 8b of the loading nut 8 isseparate from the flange section S2 of the sleeve S to form therebetweenan annular space C. Thus, the sleeve S is pressed against the stepsection 1a of the main shaft 1 under an axial force due to screwing ofthe loading nut 8 in order to provide and compensate a pressure of theloading nut 8 against the step section 1a.

In this embodiment, the axial length L of the sleeve S is larger thanthe axial length of a part P of the main shaft 1 between the annularflat face of the step section 1a and the tip end of the cylindricalprojection 8b of the loading nut 8. Additionally, the cross-sectionalarea of the cylindrical section S1 of the sleeve S is smaller than thatof the part P of the main shaft 1, the cross-sectional area being on aplane perpendicular to the axis of the main shaft 1. As a result, therigidity (or spring constant) of the sleeve S is lower than that of thepart P of the main shaft 1. Accordingly, the sleeve S is axiallycontracted or is elastically deformed along its axis upon tightening theloading nut 8 to provide the pre-load to the Belleville springs 7, sothat the axial contraction amount of the sleeve S is larger than theaxial elongation amount of the part P of the main shaft 1. Foraccomplishing the above purpose, the sleeve S may be formed of castiron, copper, aluminum, brass, or a variety of alloys containing copperand aluminum, in place of steel. However, it is preferable that thesleeve S is formed of the same carbon steel as that of the main shaft 1to obtain a predetermined hardness.

An annular cam flange 9 is rotatably mounted on the main shaft. Aloading cam mechanism 10 is provided between the cam flange 9 and theinput disc 2a.

With the above toroidal continuously variable transmission T, arotational force is transmitted from an input shaft 11 to the cam flange9 through a so-called forward and backward changing mechanism 12. Therotational force transmitted to the cam flange 9 is further transmittedthrough the loading cam mechanism 10. When relative rotation is madethrough the loading cam mechanism 10 between the cam flange 9 and theinput disc 2a, the loading cam mechanism 10 produces a thrust forthrusting the input disc 2a toward the output disc 3a. A reaction forceof the above thrust is input from the cam flange 9 to the other inputdisc 2b via a bearing 13, the main shaft 1, the loading nut 8 and thebelleville springs 7, thereby producing a thrust directing to the outputdisc 3b. The thrusts (based on a transmitted torque from the input shaft11) transmitted through the loading cam mechanism 10 to the input discs2a, 2b cause each power roller 4a, 4b, 5a, 5b to be put between andbrought into frictional engagement with the input and output discs 2a,3a (2b, 3b) under pressure corresponding to the transmitted torque fromthe input shaft 11, thus transmitting power from the input shaft 11 tothe output disc 3a, 3b.

It will be understood that the main shaft 1 may axially elongate orelastically deform along its axis when a large torque change is madeduring vehicle speed change, so that the part P of the main shaft 1 alsoelongates to increase the distance between the step section 1a of themain shaft 1 and the tip end of the cylindrical projection 8b of theloading nut 8. However, by virtue of the sleeve S which is in presscontact with the step section 1a of the main shaft 1 in the contractedstate, no space is produced between the main shaft step section 1a andthe sleeve S so as to thereby prevent the loading nut 8 from beingloosened, even though the main shaft 1 axially elongates.

Effects of the present invention will be discussed in detail incomparison with a conventional toroidal continuously variabletransmission shown in FIG. 2.

In the conventional toroidal continuously variable transmission shown inFIG. 2, a loading nut 14 screwed and fixed on a main shaft 1' to bebrought into press contact with a step section 1a' of the main shaft 1'is higher in rigidity (or spring constant) and difficult to have asufficient axial length of its internal threaded portion from theviewpoint of construction of the transmission. Additionally, it is alsodifficult that the length L1 of an abutting end section 14a of a loadingnut 14 is sufficiently large to compensate the tightening force of theloading nut 14. Under such a situation, when relative rotation (in anamount corresponding to play of a ball spline 15 in the rotationaldirection) is made between an input disc 16 (corresponding to the inputdisc 2b in FIG. 1) and the loading nut 14 while the main shaft 1'axially elongates owing to a thrust under an input torque, the tip endof the abutting end section 14a of the loading nut 14 separates from thestep section 1a' and therefore the loading nut will be loosened.

However, according to the toroidal continually variable transmission Tof this embodiment, the thin and axially long sleeve S is disposedbetween the step section 1a of the main shaft 1 and the loading nut 8under the contracted state so as to provide and compensate the pressureof the loading nut 8 against the step section 1a of the main shaft 1.Accordingly, the sufficient large distance L for providing the pressureagainst the main shaft step section 1a is obtained. In contrast, in theabove conventional transmission, the corresponding distance L1 isconsiderably smaller than that L of the embodiment of the presentinvention. Additionally, the cross-sectional area of the cylindricalsection S1 of the sleeve S is considerably smaller than that of theabutting end section 14a of the loading nut 14 and smaller than that ofthe part P of the main shaft 1. As a result, the rigidity (or springconstant) of the sleeve S is considerably lower than that of theabutting end section 14a of the loading nut 14 of the conventionaltransmission, so that the sleeve S can be set in position in thecontracted state under a compressive force applied from the loading nut8. Accordingly, if the main shaft 1 of the transmission T of thisembodiment makes its elastic deformation and elongates upon receiving alarge torque change during operation of the transmission T, the sleeve Sin the contracted state makes its axial restoration so that no space isproduced between the step section 1a of the main shaft 1 and the sleeveS to maintain a suitable pressure of the sleeve S against the annularflat surface of the main shaft step section 1a. Thus, the loading nut 8can be effectively prevented from being loosened.

Furthermore, in the conventional toroidal continuously variabletransmission shown in FIG. 2, during operation of the transmission, thebelleville springs 7' make their axial sliding movement and contractionon the cylindrical section of the loading nut 14, in which thecylindrical section is subjected to a large amount of wear owing tosliding contact between it and the belleville springs 7'. In view ofthis, the peripheral surface portion of the cylindrical section of theloading nut 14 is usually hardened, for example, by carburizing. Inmaking such a hardening processing to the loading nut 14, it isnecessary to make a precise control in order to avoid a strengthdegradation (depending on hardening) of the internal thread portion ofthe loading nut 14, thereby complicating the production process of theloading nut 14.

However, according to the transmission T of this embodiment, it issufficient to make a hardening process (such as carburizing) only on thesleeve S without making the hardening process on the loading nut 8. Thissimplifies the production process of a loading unit including theloading nut 8 and the sleeve S. In this regard, it is preferable thatthe outer peripheral surface portion of the sleeve S is subjected to asurface hardening treatment such as carburizing or a hardening in orderto prevent the sleeve S from being worn under sliding contact with theinner peripheral portion of each belleville spring 7.

Besides, the sleeve S has the flange section S2 which extends radiallyinward to reach a position corresponding to the bottom of a groove forthe balls of each ball spline Bs2, thereby enlarging the contacting areaof the sleeve S to the main shaft step section 1a. This prevents thepressure of the sleeve S against the main shaft step section 1a fromexcessively increasing, thus avoiding plastic deformation of respectiveparts abutting to each other. Additionally, the internal thread portionof the loading nut 8 extends axially deeply inside the cylindricalsection S1 of the sleeve S so as to increase the axial dimensionthereof, thus further preventing the loading nut from being loosened.

FIG. 3 illustrates another embodiment of the toroidal continuouslyvariable transmission T according to the present invention, similar tothe embodiment of FIG. 1, in which the assembled state of the main shaft1, the loading nut 8 and the sleeve S is the same as that of theembodiment of FIG. 1. In this embodiment, an annular shim 17 foradjusting preload to the belleville springs 7 is mounted on thecylindrical section S1 of the sleeve S and disposed between the annularflat face of the loading nut 8 and two belleville springs 7 which are incontact with the input disc 2b. It will be appreciated that the loadingnut 8 can be effectively prevented from being loosened, as same as inthe embodiment of FIG. 1.

FIG. 4 illustrates a further embodiment of the toroidal continuouslyvariable transmission T according to the present invention, which issimilar to the embodiment of FIG. 1, in which the assembled state of themain shaft 1, the loading nut 8 and the sleeve S is the same as that ofthe embodiment of FIG. 1. In this embodiment, the sleeve S is providedwith the function of the spacer or the shim for adjusting the pre-loadupon omitting the spacer and the shim, and the internal thread portionof the loading nut 8 is extended in an opposite direction of thecylindrical projection 8b or toward an output gear (no numeral). In thiscase, while it is required to precisely set the axial length of thesleeve S in order to secure the screwing amount of the loading nut 8 andthe adjusting amount of the pre-load to the belleville springs 7, notonly the number of parts of the transmission T can be reduced but alsothe input disc 2b is not required to be formed with a groove forinsertion of the spacer, thereby making it possible to increase thethickness of the input disc 2. In case that the groove for insertion ofthe spacer is formed, the internal thread portion of the loading nut 8can be extended also toward the input disc. Thus, strength of thecomponent parts of the transmission T can be improved in any case.

While the double cavity type toroidal continuously variabletransmissions T have been shown and described as the embodiments, itwill be appreciated that the principle of the present invention may beapplied to a variety of transmissions of the type wherein the fasteningforce of a nut is lowered under a thrust acting on a main shaft.

I claim:
 1. A toroidal continuously variable transmission comprising:a main shaft having a step section; an input disc drivably supported on the main shaft and movable axially along an axis of the main shaft; an output disc rotatably supported on the main shaft and located facing said input disc; a power roller disposed between and in frictional engagement with said input disc and said output disc so as to make transmission of power from said input disc to said output disc; belleville springs each having a center opening, said belleville springs being disposed around the main shaft and located at an opposite side of said input disc with respect to said output disc so as to press said input disc toward said output disc; a loading nut screwed on the main shaft to restrict an expansion amount of the belleville springs, said loading nut axially facing the step section of said main shaft; and a sleeve disposed between said loading nut and the step section of the main shaft, said sleeve being separable from said loading nut, said sleeve being disposed around the main shaft and having a major part clear of the main shaft, said belleville springs abutting said sleeve in a manner that said sleeve passes through the central opening of each belleville spring.
 2. The toroidal continuously variable transmission as claimed in claim 1, wherein said sleeve has an axial length which is larger than an axial length of a part of said main shaft between the step section and an axial end of said loading nut.
 3. The toroidal continuously variable transmission as claimed in claim 1, wherein said sleeve has a section having a cross-sectional area which is smaller than a cross-sectional area of a part of said main shaft between the step section and an axial end of said loading nut, each cross-sectional area being on a plane perpendicular to the rotational axis of said main shaft.
 4. The toroidal continuously variable transmission as claimed in claim 1, wherein said sleeve is formed of a metal material which is lower in rigidity than a metal material of said main shaft.
 5. The toroidal continuously variable transmission as claimed in claim 1, wherein said main shaft includes a first section on which said input and output discs are supported, and a second section which is smaller in outer diameter than said first section, said loading nut and said sleeve being mounted on said second section, wherein the step section is formed at a border between said first and second sections, the step section having an annular face facing said loading nut.
 6. The toroidal continuously variable transmission as claimed in claim 5, wherein said loading nut includes an annular main body section threadedly engaged on said second section of said main shaft, and a cylindrical projection which is integral and coaxial with said main body section, said cylindrical projection projecting toward the annular face of the step section and being smaller in outer diameter than said main body section.
 7. The toroidal continuously variable transmission as claimed in claim 6, wherein said sleeve includes a cylindrical section coaxial with said main shaft and mounted on said cylindrical projection of said loading nut, said belleville springs being slidably mounted on an outer peripheral surface of said cylindrical section, and a flange section integral with said cylindrical section and extending radially inward to contact with an outer peripheral surface of said main shaft second section, said flange section being in press contact with the annular face of the step section, said flange section being separate from said cylindrical projection of said loading nut to form a space.
 8. The toroidal continuously variable transmission as claimed in claim 7, wherein said sleeve has an axial length which is larger than an axial length of a part of said main shaft between the step section and an axial end of said loading nut.
 9. The toroidal continuously variable transmission as claimed in claim 8, wherein said cylindrical projection of said loading nut is axially inserted into said cylindrical section of said sleeve so that a tip end thereof is located generally at the axially central part of said cylindrical section, wherein said loading nut is formed with an internal thread portion which extends throughout said main body section and said cylindrical projection.
 10. The toroidal continuously variable transmission as claimed in claim 7, wherein said sleeve is formed of a metal material which is lower in rigidity than a metal material of said main shaft.
 11. The toroidal continuously variable transmission as claimed in claim 7, wherein said cylindrical section of said sleeve has a cross-sectional area which is smaller than a cross-sectional area of a part of said main shaft between the step section and an axial end of said loading nut, each cross-sectional area being on a plane perpendicular to the rotational axis of said main shaft.
 12. The toroidal continuously variable transmission as claimed in claim 1, wherein said sleeve has an outer peripheral surface portion on which said belleville springs are slidably mounted, at least said outer peripheral surface being hardened by a hardening treatment.
 13. A toroidal continuously variable transmission comprising:a main shaft having a step section; an input disc drivably supported on the main shaft and movable axially along an axis of the main shaft; an output disc rotatably supported on the main shaft and located facing said input disc; a power roller disposed between and in frictional engagement with said input disc and said output disc so as to make transmission of power from said input disc to said output disc; belleville springs each having a center opening, said belleville springs being disposed around the main shaft and located at an opposite side of said input disc with respect to said output disc so as to press said input disc toward said output disc; a loading nut screwed on the main shaft to restrict an expansion amount of the belleville springs, said loading nut axially facing the step section of said main shaft; and a sleeve disposed between said loading nut and the step section of the main shaft and disposed around said main shaft, said sleeve being separable from said loading nut, said belleville springs abutting said sleeve in a manner that said sleeve passes through the central opening of each belleville spring, said sleeve having a flange section located around said main shaft and extending radially inward toward an outer peripheral surface of said main shaft, said flange section being in contact with the step section of said main shaft, and a cylindrical section integral and coaxial with said flange section, said cylindrical section being larger in axial length than said flange section and radially clear of the outer peripheral surface of said main shaft, said cylindrical section being in contact with said loading nut. 